In the 1920s, many rural banks failed because farmers could not repay their loans. Option B is correct.
In the 1920s, many rural banks failed because of the failure of the farms to produce the bumper crops they were producing previously. The farmers had invested too much money in machinery as well as storage facilities. Howeverm the production decreased so that they failed to make enough profit, investment did not recover and they failed to pay their loans back.